The present invention relates to a carrier formed of stereocomplexes of polymers for delivery of bioactive or bioreactive molecules.
Priority is claimed to Israeli patent application Serial No. 122933, filed on Jan. 14, 1998.
Much research has focused on the development of materials which are biocompatible and degrade chemically or enzymatically in vivo to inert or normal metabolites of the body. The preferred material degrades completely in vivo so there is no need to remove the device at the end of treatment. Direct implantation of a drug loaded device is particularly useful for drugs that undergo first pass metabolism. Linear polyesters of lactide and glycolide have been used for more than three decades for a variety of medical applications, including delivery of drugs. Handbook of Biodegradable Polymers, A. Domb, J. Kost and D. Wiseman, Harwood and Brooks (1997). Extensive research has been devoted to the use of these polymers as carriers for controlled drug delivery of a wide range of bioactive agents for human and animal use. Injectable formulations containing microspheres of lactide/glycolide polymers have received the most attention in recent years.
Polymer characteristics are affected by the monomer types and composition, the polymer architecture, and the molecular weight. The crystallinity of the polymer, an important factor in polymer biodegradation, varies with the stereoregularity of the polymer. For example, racemic D,L poly(lactide) or poly(glycolide) is less crystalline than the D or L homopolymers. Poly(lactide) (PLA) and its copolymers having less than 50% glycolic acid content are soluble in common solvents such as chlorinated hydrocarbons, tetrahydrofuran, and ethyl acetate while poly(glycolide) (PGA) is insoluble in common solvents but is soluble in hexafluoroisopropanol.
PLA has wide applications in medicine because of its biocompatibility and degradability to nontoxic products. Micelles and particles of the AB block copolymer poly(lactide)-b-poly(ethyleneglycol) (PLA-b-PEG) have received attention for use in intravenous injectable delivery systems for extended and target drug release. Gref, R. et al., Protein Delivery-Physical Systems, L. M. Sanders and H. Hendren, Eds, Plenum Press, (1997); and Gref, R. et al., Advanced Drug Delivery Reviews, 16: 215-233 (1995). Similarly, U.S. Pat. No. 5,578,325 to Domb et al. teaches multiblock copolymers comprising a multifunctional compound covalently linked with one or more hydrophilic polymers and one or more hydrophobic bioerodible polymers and including at least three polymer blocks. A PEG-coating on a microparticle or other polymeric device prevents the adsorption of plasma proteins and fast elimination by the reticulo endothelial system (RES). Possible applications for this kind of pharmaceutical depot devices are the delivery of drugs with short half-lives, transport of contrast agents, chemotherapy, and gene therapy.
AB-block copolymers of poly(styrene)-b-poly(acrylic acid) (PS-b-PAA) produce vesicle type particles which can be isolated from solution. Zhang, L. et al., Science (1995) 268, 1728. The vesicles have diameters up to 1 micron, which is much larger than that of a single micelle. This is explained by the irreversible formation of the vesicles by the fusion of micelles. However, once the micelles are associated, the high Tg of poly(styrene) (PS) freezes the structure since the PS-blocks are no longer in equilibrium with the solvent and the structure is still stable after removing the solvent. Vesicular architecture of block copolymers would appear to offer future opportunities for pharmaceutical drug devices. Nevertheless, PS and PAA cannot be used as biodegradable carriers because they are stable and do not degrade in biological mediums.
There is still a great need for a safe and effective delivery systems for labile and/or large molecules such as bioactive peptides, proteins, plasmid genes and antisense molecules, to be delivered to specific targets (tissue, cells or nucleus). Present methods are ineffective and result in poor transfection yield and toxicity when the carrier is a polycation. The major problems in the delivery of peptide and proteins are due to their instability and fast release from the polymer matrix.
It would be advantageous to have better polymeric carriers for macromolecules such as peptides, proteins, and nucleic acids.
It is therefore an object of the present invention to provide novel polymer-bioactive compositions and formulations having desirable properties for controlled and/or sustained drug delivery.
It is a further object of the present invention to provide materials which can be formulated into nano- and micro-structures for use as carriers for controlled drug delivery.
It is still another object of the present invention to provide methods for use of these compositions in the selective and extended release administration of bioactive small molecules and macromolecules such as peptides, proteins, and polynucleotides (antisense and genes).
A polymeric carrier for delivery of bioactive or bioreactive molecules is provided, including a stereocomplex of one or more biocompatible polymers and having incorporated on or within the complex the molecules to be delivered. In a preferred embodiment, the biocompatible stereoselective polymers are linear or branched D-PLA homo- and block-polymers, linear or branched L-PLA homo- and block-polymers, copolymers thereof, or mixtures thereof, in stereocomplexed form. In one preferred embodiment the polymeric carrier is complexed with a complementary stereospecific bioactive molecule. In other embodiments, the bioactive, or bioreactive (for example, for use in diagnostic applications), is bound to the complex by ionic, hydrogen, or other non-covalent binding reactions not involving stereocomplexation, or is physically entrapped within the complex, either at the time of complex formation or when the polymeric material is formulated into particles, tablets, or other form for pharmaceutical application. Exemplary bioactive molecules include peptides, proteins, nucleotides, oligonucleotides, sugars, carbohydrates, and other synthetic or natural organic molecules, as well as stereoselective drugs of a molecular weight of 300 Dalton or higher.
Examples demonstrate preparation of stereocomplexes, as well as their use for controlled and/or sustained release.
Stereocomplexation of macromolecules to biodegradable polymers is a new approach in the delivery of macromolecules. The interaction at the molecular level between the polymer carrier and the bioactive macromolecule provides stability, which allows for extended release and for easy access to the target cell or tissue with minimal toxicity.
The formation of stereocomplexes between enantiomorphic PLAs and blends has previously been investigated by Cramer, K. et al., Polymer Bulletin 35:457-464 (1995); Brizzolara, D. et al., J. Computer-Aided Meter. Design, 3:341-350 (1996); and Brizzolara, D. et al., Macromolecules, 29:191 (1996). Stereocomplexes including a racemic packing of enantiomorphic poly(L-lactide) [L-PLA] and poly(D-Lactide) [L-PLA] have a melting point 60xc2x0 C. higher than chiral crystals with the packing of isomorphic PLA""s. As a consequence of the different packing, the chiral and racemic single crystals exhibit different morphologies. The stereocomplex forms lamella triangular or rounded hedrite type crystals instead of lozenge shaped crystals.
In contrast, as described herein in the examples, PLA-b-PEG aggregates to supra molecular assemblies like flat or tubular rods of hundreds of nanometers wide and a few microns long. Powder-diffraction patterns indicate that the crystallization of both blocks are the driving force for the formation of the mesoscopic suprastructures. The crystallized blocks are not in equilibrium with the solvent for very long, which explains the stability of the structures after removing the solvent. In combination with the racemic crystallization of the PLA-blocks, vesicle type particles emerge from dioxane and acetonitrile solutions. The racemic particles of PEG-b-L-PLA/PEG-b-D-PLA should have a similar assembly to the PS-b-PAA particles. The racemic particles of PEG-b-PLA have a much higher potential as a drug carrier system because of the safety of the polymer and its degradation products. The hydrophobic content within the vesicles should support the encapsulation of non-polar drugs. The hydrophobic/hydrophilic content may provide a type of target mechanism to pass through lipid membranes.
The constitution of PLA and peptides is similar, with the exception that PLA is a polyester and peptides are polyamides. Esters cannot form hydrogen bonds to each other since they lack hydroxyl groups. In organic solvents poly(amino acids) do not form hydrogen bonds. Thus the crystallization and packing of poly(amino acids) is comparable to PLA. Enantiomorphic poly(alanine) and PLA were crystallized into a racemic lattice to better understand the specific interactions between peptides and synthetic polymers. Until now only microparticles of the statistical copolymer poly(lactide)-b-poly(glycolide) containing LHRH showed the delayed liberation of the hormone. The specific interactions between the polymer and LHRH is the reason for the strong adhesion to the polymer matrix. A deeper understanding of the kind of interactions between peptides and polymers is necessary so that other peptides which can be encapsulated effectively, like LHRH, can be identified.
The initial results from force field simulation are promising. They demonstrate that the interaction energy between enantiomorphic poly(alanine) and PLA is greater than between isomorphic PLA. Based on the force-field calculation results, the racemic crystallization between poly(alanine) and PLA is favored compared to the separate crystallization.
I. Polymeric Carriers
Polymers
Polymeric carriers are provided for delivery of bioactive or bioreactive molecules, which include at least one biocompatible stereoselective polymer. Examples of useful polymers include polyhydroxy acids, polyhydroxyalkyls, polyalkylene oxides, polyesters, polycarbonates, and polyanhydrides. In a preferred embodiment, the carrier is formed from linear or branched D-PLA homo- or block-polymers, linear or branched L-PLA homo- or block-polymers, copolymers thereof and mixtures thereof where the copolymers are linear or branched D-PLA or L-PLA block copolymer copolymerized with a component such as a poly(hydroxyalkyl acid), polycarbonate or polyanhydride.
Polymeric carriers can also be formed of, or include, a stereocomplex of homo- or block-copolymers of D-lactide or homo- or block-copolymers of L-lactide with inert polyamino acids (such as polyalanine or polylysine), polypeptides or polysaccharides. The block length of the enantiomeric segment is typically equivalent to ten lactide units or more.
Examples of proteins or polyamino acids that are particularly useful as components in stereocomplexes include albumin, gelatin, collagen, fibrinogen, polyalanine, polyglycine, and polylysine.
Polymers which are particularly useful for stereocomplexation in gene therapy are those with a stereoselective structure with cationic sites that allow a plasmid to be complexed by diasteriomer formation and by electrostatic complexation. Representative polymers are: D-PLA graft and block copolymers with short polyamine such as polyethylene imine (Mw less than 2,000), poly(lysine), spermine, spermidine and copolymers of D-lactide and D-lysine.
Methods for Making Polymers and Polymer Complexes
The general synthetic procedures for the synthesis of the polymers is as follows. Polymers are dissolved in a suitable solvent and appropriate polymerization catalysts such as short alcohols, polyethylene glycol (PEG), fatty alcohol or polyalcohol, added in a range such as 0.1 to 3 mole percent per lactide. The solvent is removed after polymerization is initiated, for example, by solvent evaporation The molar ratio between the monomer and the catalyst determine the polymer block molecular weight. The length and number of blocks is controlled by the number of and amount of each monomer units added and the amount of catalyst used.
Alternatively, pre-prepared polymer blocks with hydroxyl and carboxylic acid can be conjugated via an ester, phosphate, anhydride, or carbonate bond. The hydroxyl end groups are reacted with either a diacid chloride (i.e. adipoyl chloride, sebacoyl chloride), alkyl phosphodichloridate, or phosgene to form ester, phosphate or carbonate block conjugates, respectively. Anhydride copolymers are prepared by activating the PLA carboxylic acid end group with acetic anhydride and copolymerized with sebacic acid prepolymer according to Domb et al., J. Poly. Sci. 25:3373 (1987). Multiblock copolymers of PLA are prepared by using a polyalcohol such as pentaerythritol, or glycerol in the catalyst mixture. The structures and block length can be determined by H-NMR and GPC. Typical MW of polymers is in the range of 5,000 to 100,000.
For example, homopolymers of PLA were synthesized by dissolving D-lactide or L-lactide in dry toluene at 100xc2x0 C. and adding a solution of stannous octoate and alcohol as polymerization catalyst (5% solution in toluene, 0.1 to 3 mole % per lactide). After 3 hours the solvent was evaporated to dryness and the viscous residue was left at 130xc2x0 C. for additional 2 hours to yield the polymer. When lactide block copolymers were prepared, the first block, i.e. L-lactide, was prepared in toluene at 100xc2x0 C. and a second portion of lactide, i.e. D-lactide, was added and polymerization continued for an additional 2 hours; then a third portion of lactide was added and the polymerization continued. Block copolymers with cyclic hydroxy alkyl acids and cyclic carbonates are prepared in a similar manner, but the second portion is the desired cyclic monomer (caprolactone, trimethylene carbonate, glycolide), instead of lactide.
A tetrablock copolymer consisting of two D-PLA chains and two L-PLA chains was prepared by polymerizing D-lactide with dibenzyl tartarate using stannous octoate as catalyst. After polymerization at 130xc2x0 C. as described above, the benzyl protecting groups were removed by hydrolysis or hydrogenation. The free acid groups were esterified with hydroxyl terminated L-PLA in chloroform solution and DCC as coupling agent. The length of the blocks varied depending on the amount of D-lactide used for polymerization and the L-PLA chain length. This polymer formed an intra and inter-stereocomplexation. Other multiblock polymers contained blocks of either or both D-PLA and L-PLA and other biodegradable polymers or poly(oxyalkanes) or contained other branching molecules like mucic acid, pentaerythritol, citric acid and malonic acid 2-methanol.
To form stereocomplexes, polymer is either dissolved in a solvent in which the polymers are soluble or the polymer components melted together. The polymer mixture is stored under conditions at which the polymers will complex and precipitate out of solution, or cool. The mixture can be formed into a desired shape as it forms, or processed after stereocomplex formation.
Solvents which can be used to dissolve polymers for formation of stereocomplexes include dioxane, chloroform tetrahydrofuran, ethyl acetate, acetone, N-methylpyrrolidone, ethyl and methyl lactate, ethyl acetate and mixtures of these solvents, and other solvents, such as water, short chain alcohols and carboxylic acids (C5 or below). The particle size of the precipitate is controlled by the selected solvent, the drug, and polymer concentrations, and the reaction conditions (temperature, mixing, volume etc.).
As demonstrated by the following examples, a range of copolymers containing stereoselective blocks of enantiomorphic PLA were synthesized and used to form nanoscale structures resulting from specific stereocomplexations. Block copolymers containing blocks of D-lactide and L-lactide, as shown in Table 1, were synthesized. Polymer blocks of molecular weights ranging from 600 to 100,000 daltons were prepared; their molecular weights were estimated by gel permeation chromatography (GPC) and determined by 1H-NMR. L-PLA blocks of 20 to 100 lactide units were conjugated to a biodegradable polyanhydride, polycaprolactone and polyhydroxybutyrate, or to the hydrophilic poly(ethylene glycol) or poly(propylene glycol). The stereocomplexation of these copolymers with short and long chain polymers of D-lactide at different solutions and conditions was characterized by atomic force microscopy (AFM) and related surface characterization methods (SEM, TEM, XPS). The interaction of poly(D-lactide) and its copolymers with peptides and oligonucleotides to form spontaneous nanoparticles was evaluated as a delivery system to tissues or to cells. Other block copolymers of PLA, such as diblock copolymers of D-PLA-co-L-PLA were also prepared in the manner stated above, using the proper solvents.
Table 1: Structures of Block Copolymers
a. Lactide Copolymers
homopolymers of (D-LA)x or (L-LA)xx=10 to 5,000
block copolymers of [(D-LA)x-X-(L-LA)y]z 
where x, y=10 to 5,000 and z=0 to 100
block copolymers of [(DL-LA)x-X-(L-LA)y]z 
where x, y=10 to 5,000 and z=0 to 100
block copolymers of [(D-LA)x-X-(DL-LA)y]z 
where x, y=10 to 5,000 and z=0 to 100
block copolymers of [(D-LA)x-X-(DL-LA)y]z 
where x, y=10 to 5,000 and z=0 to 100
X=ester, carbonate, ether, phosphate, anhydride, orthoester, or a branching molecule
b. PLA-polyanhydride Copolymers
block copolymers of [(D-LA)x-co-(COOxe2x80x94Rxe2x80x94CO)y]z 
where x, y=10 to 5,000 and z=0 to 100
R=aliphatic, aromatic or heterocyclic residue
block copolymers of [(L-LA)x-co-(COOxe2x80x94Rxe2x80x94CO)y]z 
where x, y=0 to 5,000 and z=0 to 100
R=aliphatic, aromatic or heterocyclic residue
c. PLA-poly(hydroxy Alkyl Acid) and Carbonate Copolymers
block copolymers of [(D-LA)x-co-(COxe2x80x94Rxe2x80x2xe2x80x94O)y]z 
where x, y=10 to 5,000 and z=0 to 100
Rxe2x80x2=(CH2)1-5, CH(CH2xe2x80x94CH3)CH2, Oxe2x80x94(CH2)2-3 
block copolymers of [L-LA)x-co-(COxe2x80x94Rxe2x80x2xe2x80x94O)y]z 
where x, y=10 to 5,000 and z=0 to 100
Rxe2x80x2=(CH2)1-5, CH(CH2xe2x80x94CH3)CH2, Oxe2x80x94(CH2)2-3 
d. PLA-poly(ethylene and Propylene Oxides) Copolymers
block copolymers of [(D-LA)x-co-(Oxe2x80x94CH2xe2x80x94CH2)y]z 
where x, y=10 to 5,000 and z=0 to 100
block copolymers of [(D-LA)x-co-(Oxe2x80x94CH2xe2x80x94CH(CH3))y]z 
where x, y=10 to 5,000 and z=0 to 100
block copolymers of [(L-LA)x-co-(Oxe2x80x94CH2xe2x80x94CH2)y]z 
where x, y=10 to 5,000 and z=0 to 100
block copolymers of [(D-LA)x-co-(Oxe2x80x94CH2xe2x80x94CH(CH3))y]z 
where x, y=10 to 5,000 and z=0 to 100
e. PLA Multiblock Copolymers
multiblock copolymers [(D-LA)x]a-X-[(Oxe2x80x94CH2xe2x80x94CH2)y]b 
where x, y=10 to 5,000 and a, b=1 to 6
X=tartaric acid, mucic acid, citric acid
multiblock copolymers [D-LA)x]a-X-[L(L-LAx]b)
where x, y=10 to 5,000 and a, b=1 to 6
X=penaerytritol mono- and polysaccharides glycerin
II. Pharmaceutical Formulations
Bioactive Molecules
The stereocomplexes can be used to deliver any of a variety of molecules which may broadly be classed as bioactive or bioreactive molecules, for therapeutic, prophylactic or diagnostic applications, referred to generally herein as xe2x80x9cbioactive moleculesxe2x80x9d. In some cases one or more of the polymeric components of the stereocomplex will consist of the bioactive molecules. Bioactive molecules can be any of the broad chemical classes of peptides, proteins, sugars, carbohydrate, lipids, nucleotides, oligonucleotides, and combinations thereof such as glycoproteins. Examples of preferred bioactive molecules include hormones, clotting factors, proteases, growth factors; and vaccines. Examples of peptides include hormones such as LHRH, GNRH, enkephalin, ACTH, a-MSH, somatostatin, calcitonin, insulin and their analogs. Examples of proteins include erythropoeitin, t-PA, Factor VIII, growth hormone, growth factors like FGF, BMP, and EGF; and vaccines against bacterial or viral pathogens such as vaccines containing as antigens staphylococcal enterotoxin B toxoid, HGC-DT, diphtheria toxoid and ribonuclease A. Examples of preferred oligonucleotides include antisense, genes, plasmids and viral vectors.
Formulations
The bioactive molecules can be incorporated onto or into the stereocomplexes. They can be coupled to the stereocomplexes by ionic, hydrogen or other types of bond formation, including covalent bond formation. The bioactive molecules can be incorporated into the stereocomplexes when the polymers are mixed together in solution or melted, so that the molecules are entrapped within the polymer complex as it precipitates or cools. They can also physically be mixed with the stereocomplexes as these are formulated into tablets, molds, or particles, as described below. Alternatively, the bioactive molecules can be coupled to the stereocomplexes after formation of the complexes or the formulations containing the complexes.
The stereocomplexes are typically formed into devices for drug delivery using standard polymer processing techniques to form particles including nanoparticles, microspheres, and microcapsules, pellets, tablets, films, rods, or beads. Alternatively, the polymers can be formulated into a paste, ointment, cream, gel, or transdermal patch.
The polymers can also be lyophilized and then formulated into an aqueous suspension in a range of microgram/ml to 100 mg/ml prior to use. Suitable vehicles include water, saline, and phosphate buffered saline.
Administration of the Stereocomplex Formulations
The bioactive or bioreactive component can be administered once, or may be divided into a number of smaller doses to be administered at varying intervals of time, depending on the release rate of the carrier and the desired dosage. The above formulation principles are well known in the art. The formulations can be administered to a patient in a variety of routes, for example, orally, parenterally, intravenously, intradermally, subcutaneously, or topically, in liquid, cream, gel, or solid form, as appropriate for the drug to be delivered.
The carrier should contain the substance to be delivered in an amount sufficient to deliver to a patient a therapeutically effective amount of compound. The desired concentration of active compound with the carrier will depend on absorption, inactivation, and excretion rates of the drug, as well as the delivery rate of the compound from the carrier. It is to be noted that dosage values will also vary with the severity of the condition to be alleviated. It is to be further understood that, for any particular subject, specific dosage regimens should be adjusted over time according to the individual need and the professional judgment of the person administering or supervising the administration of the compositions.